1. Technical Field
The present invention generally relates to the desulfurization of gas streams containing hydrogen sulfide. More particularly, the present invention relates to a high shear system and method for catalytically oxidizing hydrogen sulfide in liquid streams comprising hydrogen sulfide to elemental sulfur and regenerating reduced catalyst for recycle by oxidation.
2. Background of the Invention
Many processes produce fluid streams comprising hydrogen sulfide. Often, hydrogen sulfide must be removed from a gas prior to venting the gas for disposal or further treatment. For example, hydrogen sulfide is a nuisance odor from wastewater treatment plants and facilities comprising reverse osmosis systems. Hydrogen sulfide can also be a naturally-present component in energy sources, including natural gas, oil, biogas, synthesis gas, geothermal gas streams, and others. Hydrodesulfurization of liquid streams by hydrogen treatment in the presence of a hydrodesulfurization catalyst is frequently used to convert organic sulfur compounds to hydrogen sulfide. The hydrogen sulfide must then be removed from the liquid streams. Combustion of hydrogen sulfide produces sulfur dioxide, which is believed to lead to the production of acid rain and potential destruction of the environment. Furthermore, when contacted with water, hydrogen sulfide forms sulfuric acid which is corrosive to the metals of process apparatus.
One commercial desulfurization process is the LO-CAT process of Gas Technology Products, LLC of Schaumberg, Ill. The Lo-CAT process is a method for performing a modified Claus reaction. The Lo Cat process is a wet scrubbing, liquid redox system that uses a chelated iron solution (homogeneous catalytic, i.e. ‘LoCat’, solution) to convert H2S to elemental sulfur.
A considerable amount of effort has been devoted to developing mass transfer devices which improve the oxygen utilization in conventional liquid oxidation systems (such as the Lo-CAT system) with the aim of reducing the quantity of air required (operating cost) and reducing the size of the oxidizing vessels (capital cost). Currently, there are two types of oxidizers employed: low head and high head oxidizers. In low head oxidizers, air is sparged through approximately 3 meters of solution at superficial air velocities of less than 3.5 m/min by means of distributors equipped with EPDM (ethylene propylene diene monomer) sleeves which are perforated with very small holes. Solution flow is perpendicular to the airflow. Such low head oxidizers are relatively poor mass transfer devices. Low head oxidizers do, however, provide much needed solution inventory for proper operation of the system.
In high head oxidizers, air is sparged through approximately 7 meters of solution at superficial velocities of greater than 10 m/min by means of coarse bubble pipe distributors. Solution flow is co-current to the airflow in high head oxidizers. These oxidizers provide mass transfer coefficients which are approximately 4 times better than those of low head oxidizers; however, this is at the expense of higher discharge heads on the air blowers.
Accordingly, there is a need in industry for improved processes for desulfurizing (i.e. sweetening) gas streams.